The manufacture of disposable personal absorbent items such as diapers, absorbent pads, adult incontinence products, feminine hygiene products, etc., generates a significant amount of pre-consumer waste. Disposal of this waste is expensive due to the diminishing availability of landfill space. Incineration of the waste is undesirable, as superabsorbent polymers sometimes contained in such articles causes buildup of the polymer on the surface of the incinerator (see, e.g., U.S. Pat. No. 6,632,494 to Okubo et al.). By contrast, recycling and reuse of the waste is extremely beneficial, not only in terms of environmental benefits but also in terms of profitability for manufacturers. Because of these factors, manufacturers of disposable absorbent items are developing methods to reclaim and return as much waste as possible to the manufacturing process.
However, manufacturers face several barriers to reclaiming and reusing the waste from disposable absorbent items. One problem is that the wastes often contain a mixture of materials that are segregated in conventional manufacturing processes. For example, the waste may contain co-mingled plastics from different portions or different types of disposable articles. The co-mingled plastics may include melt-spun polypropylene, elastomeric polypropylene and polyethylene, and superabsorbent polymers, among other plastics. In addition to the co-mingled plastics, the waste can contain significant amounts of cellulosic fibers with a very low bulk density. These materials are typically segregated in manufacturing because they serve different functions.
This mixture of materials presents a challenge to reusing the waste in the manufacture of disposable absorbent items. For example, a disposable diaper typically includes a soft, porous inner liner, an absorbent layer with cellulosic fibers and superabsorbent polymers, and a moisture-resistant outer liner. The inner and outer liners cannot perform their intended functions if they are contaminated with the absorbent fibers or particles. Even when an effort is made to recycle a portion of the manufacturing waste, care is taken to prevent mixing of the recycled materials in the different portions of the manufactured article, and any mixing or contamination that occurs results in unusable absorbent articles that themselves become waste. See, e.g., U.S. Pat. No. 6,802,353 to Malakouti et al.
The mixture of materials in disposable absorbent article waste also presents challenges to reusing such waste in manufacturing other items. For example, there are several barriers to the use of the mixed waste material in the manufacture of building materials such as extruded wood plastic composites. The co-mingled plastics affect the appearance of extruded profiles made from the recycled material if the various components are not adequately and uniformly dispersed in the finished article. In addition, the cellulosic fibers are difficult to disperse in the thermoplastic, which results in clumps of fibers that are not incorporated into the thermoplastic matrix. These clumps provide areas where moisture can infiltrate the material and weaken the material. The clumps also weaken the material by resulting in discontinuities in the matrix.
Conversion of the waste into building products or consumer articles is also made difficult by the presence of superabsorbent polymers sometimes contained in such waste. The superabsorbent polymer particles absorb much more water than natural fibers. As a result, moisture is captured by the waste from ambient air. This moisture becomes a contaminant in the manufacturing process. The steam produced from this moisture during manufacturing creates voids in the interior and bubbles on the surface of extruded materials and interferes with mold-filling during the injection molding processes. The superabsorbent polymer particles attract moisture both before and after processing.
If the above barriers can be overcome, the waste from disposable absorbent articles represents a potential source of recycled fiber and thermoplastic for the manufacture of various materials, including extruded decking and siding, articles commonly made by injection molding, or processed materials such as artificial mulch. Processing these materials into usable articles requires a method of processing the waste that densifies the waste so that it can be handled, disperses the fibers and co-mingled plastics uniformly, and produces an appearance that will be acceptable to the consumer. Development of a method for processing these wastes into useful articles will benefit both the manufacturers of the disposable articles (by eliminating the cost of disposal) and the manufacturers of building materials and injection molded articles (by providing a low-cost raw material).
Various methods have attempted to recycle post-consumer waste. See, e.g., WO 2008/055149 to Reaveley and Bryant; U.S. Patent Application 2006/0006564 to Maldas et al.; and U.S. Patent Application Publication 2007/0212531 to McIntyre et al. However, these methods fail to generate articles with suitable structural integrity as a result of lacking provisions to disperse the mixed materials present in waste. Consequently, there is currently no method available for the conversion of absorbent article waste into feedstock for generating decorative or structural composites through extrusion, injection molding, or other methods.